Abstract
The present study aimed to investigate the impact of the COVID-19 pandemic on the incidence rates of psychiatric disorders using nationwide cohort data. A retrospective cohort study was conducted using South Korea's nationwide claims database, covering 1,598,540 patients with new psychiatric diagnoses from January 2017 to June 2021. We calculated incidence rate ratios pre- and during-pandemic and employed the autoregressive integrated moving average (ARIMA) model and interrupted time-series analysis to assess pandemic effects on incidence. Additionally, to determine the immediate impact of the pandemic on the observed incidence rates, we used level changes at the transition point by adopting a transfer function. The incidence rates for overall and most psychiatric disorders during the pandemic increased compared to the pre-pandemic period. However, the increases in incidence rates were due to the previous trend rather than the pandemic's impact. A notable exception was found in the diagnostic category of obsessive-compulsive disorders, which experienced a significant surge in incidence rates beyond what was predicted, indicating a direct pandemic impact. The study underscores that while the COVID-19 pandemic has influenced the incidence rates of psychiatric disorders, the effects vary significantly by disorder. The overall increase in psychiatric disorders aligns with pre-pandemic trends, except for obsessive-compulsive and substance-related disorders. Obsessive-compulsive disorders saw an actual increase in incidence rates, whereas substance-related disorders' decrease could reflect changes in healthcare-seeking behavior. The findings of this study provide valuable insights for public health planning and the development of mental health support systems in anticipation of future global health crises.